Secondary batteries that are easily applicable according to product groups and have electric characteristics such as high energy density, etc. are being commonly applied in electric vehicles (EV) or hybrid electric vehicles (HEV) driven by an electric driving source, as well as portable devices. Secondary batteries have been highlighted as a new energy source that is echo-friendly and improves energy efficiency, due to its advantages that by-products according to usage of energy do not generate at all, in addition to a primary advantage, that is, noticeable reduction in using of fossil fuel.
Secondary batteries that are widely used may include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, etc. An operating voltage of a unit secondary battery, that is, a unit battery cell, is about 2.5V to 4.2V. Therefore, in a case where an output voltage greater than above is required, a battery pack may be configured by connecting a plurality of battery cells in series. Also, a battery pack may be configured by connecting a plurality of battery cells in parallel according to charging/discharging capacity required by the battery pack. Therefore, the number of battery cells included in the battery pack may vary depending on a required output voltage or charging/discharging capacity.
In addition, in a case where a battery pack is configured by connecting a plurality of battery cells in series/in parallel, a battery module including a plurality of battery cells is configured first, and the battery pack is generally configured by using a plurality of battery modules and adding other elements.
In a battery module, in battery cell assembly including a plurality of battery cells, the battery cells may be lithium polymer pouch type secondary battery cells. In a lithium polymer pouch type secondary battery, an electrolyte in the secondary battery is decomposed as a side reaction of repeated charging and discharging operations, and a gas may be generated. Here, deformation in an exterior of the battery cell due to the generated gas is referred to as a cell swelling effect.
A battery module according to the related art includes a battery cell assembly including a plurality of battery cells and end plates covering front and rear portions of the battery cell assembly. Here, the end plate is coupled to the battery cell assembly via four corners thereof by using screw members such as shoulder bolts, in order to fixedly support the battery module and to control the cell swelling effect. Here, the screw members such as the shoulder bolts provided at four corners of the end plate fixedly compress the battery cell assembly, and prevent expansion of the battery cell assembly when the cell swelling effect occurs.
However, in the battery module according to the related art, an additional space, in which the screw members such as the shoulder bolts are arranged, and a structure for the screw coupling are necessary due to the shoulder bolts provided at the four corners of the end plate, and thus, a size of the entire module increases due to the space occupied by the screw members such as the shoulder bolts and the screw coupling structure, and it hinders slim design of the battery module.
To address this, a battery module, in which the screw member such as the shoulder bolt is provided only at a side of the end plate and an additional fixing holder of a generally U-shaped clip type is provided at the other side of the end plate so as to fix the other side of the end plate with the battery cell assembly, has been suggested. That is, the end plate and the battery cell assembly are fixed to each other by using the screw member and the fixing holder.
In the battery module of the above structure, since the screw member such as the shoulder bolt is only provided at one side of the end plate, the screw member such as the shoulder bolt may be omitted from the other side of the end plate, and thus, increase in a volume of the battery module due to the screw member may be prevented.
However, in the battery module of the above structure, the fixing holder provided at the other side of the end plate is easily loosened when the cell swelling occurs, that is, the fixing holder may be deformed and fixing power of the fixing holder may be weakened. Accordingly, the fixing holder may not bear cell swelling pressure, and deformation of the exterior of the battery module may occur.
Therefore, it is necessary to find a method of providing a slimmer battery module capable of preventing expansion of a battery cell assembly and stably fixing the battery cell assembly.